UKRAINIAN police have stormed protesters' barricades in Kiev amid violent clashes that left five activists dead, the first fatalities in two months.

Pitched battles raged in the centre of the Ukrainian capital as protesters hurled stones and Molotov cocktails at police and the security forces responded with tear gas, stun grenades and rubber bullets.

The opposition movement's medical service said that five of its activists had been killed and four of them reported found with gunshot wounds. Prosecutors have so far confirmed two deaths.

The bloody clashes marked a new peak in tensions after two months of protests over the government's failure to sign a deal for closer integration with the European Union under Russian pressure.

The epicentre of the clashes was Grushevsky Street in the city centre which has been the scene of three days of street battles between thousands of protesters and similar numbers of security forces.

Using tear gas and stun grenades, police initially pushed demonstrators back well beyond their initial lines by marching forward in military formation.

But the protesters then regrouped, creating a semi-circle of new barricades out of burning black tires whose rancid smoke filled the skies above Kiev and flames burned in near-apocalyptic scenes.

Police for the first time started moving an armoured personnel carrier towards the protesters after storming the barricades.

The security forces then used water cannon in a bid to douse the fires, but this only had the effect of causing even more smoke.

Meanwhile tens of thousands thousands on Wednesday evening filled Independence Square in Kiev which was the main protest hub for the last two months, hoping their sheer numbers would deter further action.

Klitscho warns president to yieldUkrainian President Viktor Yanukovych on Wednesday met with opposition leaders, including former world boxing champion Vitali Klitschko in a meeting that went on for several hours.

Klitschko told the crowds on Independence Square after the talks that Ukrainian protesters will go "on the attack'' if Mr Yanukovych does not swiftly offer concessions.

"If Yanukovych does not make concessions, then tomorrow (Thursday) we will go on the attack,'' Klitschko said, adding the president could resolve the situation without bloodshed by calling early elections.

He said the talks with Mr Yanukovych would continue but gave no indication they were close to any breakthrough.

Showing no mood for compromise, Ukraine's Prime Minister Mykola Azarov labelled the radical protesters behind the clashes as "terrorists''. He then headed to the World Economic Forum in Davos.

US imposes visa ban, EU warns of actionThe deadly violence horrified Ukrainians, who have never witnessed such scenes in their country including during the 2004 Orange Revolution which was almost entirely peaceful.

"The extremist part of the opposition is crudely violating the country's constitution,'' he added.

First deaths in protests"As of now, five people have been killed. Around 300 were wounded today from midnight,'' Oleg Musiy, the coordinator of the medical service, told pro-opposition Hromadske radio.

Overall, some 1700 people were injured on Wednesday and Tuesday, the protest movement said.

According to the Ukrainska Pravda news website, four of the five people found dead had gunshot wounds.

One of the activists was killed after falling from the top of the ceremonial entrance to Dynamo Kiev stadium adjacent to the protests, according to Ukrainian media.

With Ukraine supposedly celebrating its annual day of unity, Yanukovych earlier prayed for the country at a ceremony to mark the occasion, the presidency said.

The government is basing its actions on a new set of laws, which ban nearly all forms of protest in the ex-Soviet country and have enraged demonstrators.

They allow for jail terms of up to five years for those who blockade public buildings and the arrest of protesters wearing masks or helmets.

Meanwhile a prominent Ukrainian activist and journalist, Igor Lutsenko, on Wednesday appeared in public after being abducted from a hospital by unknown individuals and dumped in a forest outside Kiev.

He had been taken from a hospital in Kiev, beaten, and was eventually left in a forest by his abductors after an ordeal lasting almost a day.

Ukrainian news website Dzerkalo Tyzhnia said that two unidentified bodies had been found in the forest outside Kiev where Lutsenko had been taken after his abduction.